Synchronous condensers are used to control the "power factor" of an alternating current network. Electric lights provide a resistive load. Electric motors typically provide an inductive load contributing to a "lagging" power factor. It is helpful to add electrical equipment to the network with a "leading" power factor to counteract the lagging power factor of the motors to bring the network power factor to unity. This optimizes the distribution of alternating current. For example, as the motor load changes, as occurs with the addition of air conditioners in response to a changing heat load throughout a summer day, it is helpful to have a way to off-set the variable lagging power factor of the air conditioning motors. Large rotating synchronous condensers provide such a method.
At present, with the introduction of many co-generating electrical generating plants and the introduction of new power plants, there are a number of older and less efficient steam-turbine generators that have been or will be shut down. In some case, these generators can be used effectively as synchronous condensers.
As a general proposition, using these generators as synchronous condensers requires that the generator be disconnected from the turbine, that a thrust bearing assembly be installed on the generator rotor shaft, that there be provided a lube oil system for lubricating the thrust and journal bearings of the synchronous condenser; that there be a way slowly to increase the speed to synchronous speed and to synchronize the generator, now a synchronous condenser, to the network, and to provide a way to vary the field current, i.e., the current through the rotating field, which varies the lead or lag power factor effect.
These conditions have been addressed heretofore, and some generators have been converted. In some generators, thrust collars have been provided on the generator shaft, axially inboard of the outer ends of the shaft, when the generator was built. No thrust bearings can be employed in such a generator when it is connected to the turbine shaft, because only one thrust bearing can be used, and that one is conventionally installed at the turbine end, not at the generator end. When the turbine is disconnected from the generator, thrust bearings can be installed, using the existing thrust collars, and this operates satisfactorily. However, most generators are not so equipped. In those, several approaches have been used. In one, a thrust runner has been bolted to the drive coupling of the generator. Thrust bearings positioned on either side of a thrust collar, are held against movement by a stationery support. However, in such an arrangement, the nearest journal bearing is a generator journal bearing substantially inboard of the drive coupling, which means that there is a substantial span between the journal bearing and the outer end of the generator shaft at which the thrust bearing is positioned. High amplitude vibration has a deleterious effect upon the life of a thrust bearing so mounted and of the generator rotor. This arrangement of the thrust bearing does little or nothing to suppress high amplitude vibration of the cantilevered end of the generator rotor.
Another approach has been to machine a groove or annular channel in the generator shaft a short distance axially inboard from the drive coupling, and to install in the channel a journal bearing flanked on each side by a thrust bearing. This arrangement reduces vibration at the thrust bearing, but it has the disadvantage that the effective diameter of the shaft is reduced, so that if the generator is again connected to the turbine, the shaft has reduced torque capability.
One of the objects of this invention is to provide a synchronous condenser made from a turbine-driven generator, that will operate dependably for long periods.
Another object is to provide such a synchronous condenser which can be reattached to a turbine to operate exactly as it did before it was used as a synchronous condenser.
Another object is to provide a method of making such a synchronous condenser.
Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawing.